Aluminum silicon alloy



Patented Aug. 8, 1933 PATENT OFFICE ALUMINUM SILICON ALLOY Louis W. Kempf, Cleveland, Ohio, assignor to Aluminum Company of America, Pittsburgh, Pa., a Corporation of Pennsylvania No Drawing.

Application July 14, 1931 Serial No. 550,757

\ 3 Claims.

This invention relates to aluminum-silicon alloys such as are used principally as casting alloys but which may also be used and are often suitable for other purposes.

Aluminum-silicon alloys containing silicon in amounts ranging from 2 to 25 per cent, approximately, with or without other alloying elements, as for example magnesium, copper, nickel, manganese, etc., together with the impurities, usually iron in amounts up to about 1.5 per cent, found in commercial aluminum, possess, in general, physical properties which are well known to be highly advantageous for casting purposes,

but such alloys are apt to develop, when cast,-

areas of surface roughness composed chiefly of small projections and pits or cavities not readily removable, in some cases, by the usual finishing or polishing operations or removable only at too great an expense of time or labor. The tendency to surface roughness is thus a serious drawback, and militates against the commercial use of the alloys for casting purposes. The casting conditions that cause these rough surface effects are not well understood even by persons experienced in the art and heretofore no satisfactory method of casting aluminum-silicon alloys has been found (as far as I am aware) which will invariably produce castings of the desired freedom from the defects referred to. Moreover, castings made from aluminum-silicon alloys containing silicon in the range mentioned above are often subject to cracking on solidification, especially at the junction of a thin and a heavy section. Furthermore, it is well known that when these alloys are held in a molten condition for a time not considered unusual in the casting of other alloys, a marked impairment of the casting properties of the alloy is produced, to the consequent detriment of the physical properties and with the further effeet that the roughness and cracking, commonly found on the surface of the casting under normal casting conditions, become accentuated.

I have accordingly been led to devise my present invention, which has for its chief .object the provision of aluminum-silicon alloys of the class described, from which smooth-surfaced castings can be readily produced with substantial freedom from the cracks, pits and roughness commonly appearing on the surfaces of castings made from aluminum-silicon alloys heretofore known. Another object of the invention is to provide aluminum-silicon alloys which will not only possess the castingproperties mentioned but will also retain these'properties even after repeated remelting or after continued soaking or holding of the metal in a molten condition. y

I have discovered that these and other desirable properties may be obtained by introducing into the aluminum-silicon alloy containing up to per cent of silicon and in some cases up to per cent, a small amount of zirconium, thus making it possible to produce smooth-surfaced castings of such alloys even after the alloy has been held at a temperature of 820 C. or higher for considerable periods of time, in some cases as long as 15 hours.

The amount of zirconium required to impart these properties to aluminum-silicon'alloys is between about 0.1 and 2.0 per cent but varies alloy without zirconium. If the alloy contains 10 per cent or more of silicon, a larger amount of zirconium is needed, 0.4 per cent being usually sufficient, although about 0.2 .to 0.3 per cent of zirconium in a 10 per cent silicon alloy decidedly decreases the amount of roughness on the surface of the castings. For alloys of higher silicon content larger amounts of zirconium may be necessary, depending upon the results desired, the nature of the casting, the conditions under which the casting operation is to be carrier out, etc., but in any given circumstances the proportion of zirconium needed for the purpose can be readily ascertained and rarely should exceed'2.0 per cent.

Aluminum-silicon alloys containing zirconium are capableof being held in a molten condition and at high temperatures without losing the desirable properties produced by the zirconium. The alloys are also capable of being repeatedly remelted without appreciable impairment of their properties. The importance of this capability will be readily seen when it is remembered that it is common practice in foundries to remelt castings which for some reason are defective and can not be sold, and to also remelt the waste and trimmings, or scrap, resulting from casting operations.

It is'to be understood that the invention is not limited to the precise details specifically de- 2. An-aluminum-silicon alloy containing from about 4 to about 6 per cent silicon and from about 0.1 to 0.3 per cent zirconium, the balance being substantially all aluminum.

3. An aluminum-silicon alloy containing from about 10 to about 25 per cent silicon and from about 0.2 to about 0.4 per cent zirconium, the balance being substantially all aluminum.

LOUIS w. KEMPF. 

